The effects of biochar and hoggery biogas slurry on fluvo-aquic soil physical and hydraulic properties: a field study of four consecutive wheat–maize rotations

Purpose

The degeneration of fluvo-aquic soils due to long-term excessive fertilization is increasing in the Huang-Huai-Hai Plain, China. Products from crop straw and livestock breeding wastewater, biochar, and biogas slurry provide safe and efficient biomass resources for soil quality improvement. We assumed that biochar and biogas slurry could improve soil structure and soil water retention capacity for their special characteristics. The present study aimed to compare the effects of biochar and hoggery biogas slurry treatments on improvements to soil physical properties and water-holding capacity, and their different driving mechanisms.

Materials and methods

This study was based on a field experiment of four consecutive winter wheat–summer maize rotations on the Huang-Huai-Hai Plain, China. Using the principle of equal nitrogen inputs, three treatments were conducted: conventional farming fertilizers, biochar, and hoggery biogas slurry. The differences in indicators such as soil bulk density, total porosity, aggregate structure, saturated hydraulic conductivity, and hydraulic property parameters between different treatments were compared and analyzed. The driving factors generating these differences were also discussed.

Results and discussion

Compared to conventional fertilization, soil bulk density decreased under biochar and hoggery biogas slurry treatments, whereas soil total porosity increased after hoggery biogas slurry treatment. In the 0–20-cm soil layer, biochar treatment increased the content of >2-mm macrosoil aggregates and hoggery biogas slurry treatment increased the content of 0.25–0.5 or 1–2-mm soil aggregates. The soil saturated hydraulic conductivity in the 0–20-cm soil layer did not change significantly with biochar application, but increased with hoggery biogas slurry treatment. The application of biochar and hoggery biogas slurry improved the water-holding capacity, increasing the field capacity by 15.34 and 13.83 %, and the available water content by 16.20 and 25.87 %, respectively, in the 0–20-cm soil layer.

Conclusions

Both biochar and hoggery biogas slurry treatments significantly improved soil structure and water-holding capacity. Biogas slurry treatment significantly increased soil saturated hydraulic conductivity, soil aggregate content, while biochar treatment significantly decreased bulk density and increased total porosity of the soil.

     

Biochar use in a legume–rice rotation system: effects on soil fertility and crop performance

The aim of this study was to determine whether by applying biochar, it is possible to augment the beneficial effects of legume–crop rotation systems on soil fertility and crop performance. Repeated experiments were established in 2012 and 2013 in South-western Benin using a split-split plot design. Two legumes, Mucuna pruriens (mucuna) and Vigna unguiculata (cowpea), were planted for 42 days on biochar-amended and unamended plots and subsequently cut and applied as mulch 5 days before planting rice. Rice plants were either fertilized or not using a fertilizer rate of 60, 30, and 30 kg ha^?1 of N, P₂O₅, and K₂O, respectively. The results showed that the application of legume green manures and fertilizer, either singly or in combination, improved soil nutrient availability, CEC, shoot yield, and grain yield of rice on both biochar-amended and unamended plots. However, the effect was significantly (p < 0.05) greater on biochar-amended plots. The mean grain yield for all cropping seasons was 1.8 t ha^?1 for biochar-amended plots and 1.3 t ha^?1 for unamended plots. The greater grain yield of rice on biochar-amended plots was associated with improved soil fertility and increased N uptake.     

Effect of 46 years' application of fertilizers,FYM and lime on physical,chemical and biological properties of soil under maize–wheat system in an acid Alfisol of northwest Himalayas

Imbalanced fertilizer use with intensive cropping has threatened the sustainability of agroecosystems, especially on acid soils. An understanding of the long-term effects of fertilizers and amendments on soil health is essential for sustaining high crop yields. The effects of application of fertilizers, and amendments for 46 years on soil properties and maize yield in an acid Alfisol were investigated in this study. Ten fertilizer treatments comprising different amounts of NPK fertilizers, farmyard manure (FYM) and lime, and one control, were replicated three times in a randomized block design. At 0–15 cm soil depth, bulk density was least (1.20 t/m³), porosity (49.8%) and water holding capacity (61.7%) were greatest in 100% NPK + FYM, corresponding to the largest organic carbon content (13.93 g/kg). Microbial biomass C and dehydrogenase activity in 100% NPK + FYM were 42% and 13.7% greater than 100% NPK, respectively. Available nutrients were significantly more with 100% NPK + FYM and 100% NPK + lime than control and other fertilizer treatments. At 15–30 cm depth, the effect of various treatments was comparable to the surface layer. Grain yield declined by 55% and 53% in 100% NPK(-S) and 100% NP, respectively, compared with 100% NPK, whereas 100% N as urea alone eventually led to crop failure. Soil porosity recorded the greatest positive correlation (r = .933**), whereas bulk density recorded a negative significant correlation (r = −.942**) with grain yield. The results suggest that integrated use of FYM/lime with chemical fertilizers is a sustainable practice in terms of crop yield and soil health, whereas continuous application of urea alone is detrimental to the soil health.     

The effects of straw return on potassium fertilization rate and time in the rice–wheat rotation

In order to investigate the effects of straw return on potassium (K) fertilizer application rate and time in the rice–wheat rotation, field experiments were conducted at three sites. The results showed that when the K rate was decreased to 70% of the recommended K dosage, crop yields showed no significant decrease. With K fertilization only at rice phase, crop yields showed no marked difference compared with that provided K fertilizer both at wheat and rice seasons. Though the NH₄OAc-extracted K and HNO₃-extracted K differed slightly among the treatments, the soil apparent K balance was negative without K fertilization. With crop straw fully incorporated, the recommended K dosage could be at least reduced by 30% at the experimental sites and the K fertilizer could be applied only at rice phase. A further hypothesis can be made that the best K rate was the amount of K took away by crop grain. In the long run, straw return combined with K fertilization would be an effective method to maintain soil K fertility and productivity.     

Twelve‐year tillage and crop rotation effects on yields and soil chemical properties in northeast Iowa

Abstract

Long‐term tillage and crop management studies may be useful for determining crop production practices that are conducive to securing a sustainable agriculture. Objectives of this field study were to evaluate the combined effects of crop rotation and tillage practices on yield and changes in soil chemical properties after 12 years of research on the Clyde‐Kenyon‐Floyd soil association in northeastern Iowa. Continuous corn (Zea mays L.) and a corn‐soybean [Glycine max L. (Herr.)] rotation were grown using moldboard plowing, chisel plowing, ridge‐tillage, or no‐tillage methods. Tillage and crop rotation effects on soil pH, Bray P1, 1M NH₄OAc exchangeable K, Ca, and Mg, total C, and total N in the top 200 mm were evaluated. Profile NO₃‐N concentrations were also measured in spring and autumn of 1988. Crop yields and N use efficiencies were used to assess sustainability. Bray P1 levels increased, but exchangeable K decreased for all cropping and tillage methods. Nutrient stratification was evident for no‐tillage and ridge‐tillage methods, while the moldboard plowing treatment had the most uniform soil test levels within the 200 mm management zone. Chisel plowing incorporated fertilizer to a depth of 100 mm. Soil pH was lower with continuous corn than with crop rotation because of greater and more frequent N applications. Profile NO₃‐N concentrations were significantly different for sampling depth and among tillage methods in spring 1988. In autumn the concentrations were significantly different for sampling depth and for a rotation by tillage interaction. Estimated N use efficiencies were 40 and 50 kg grain per kg N for continuous corn, and 48 and 69 kg grain per kg N for rotated corn in 1988 and 1989, respectively. The results suggest that P fertilizer rates can be reduced, but K rates should probably be increased to maintain soil‐test levels for this soil association. Crop rotation and reduced tillage methods such as ridge‐tillage or chisel plowing appear to meet the criteria for sustainable agriculture on these soils.     

In situ immobilization of Cr and its availability to maize plants in tannery waste–contaminated soil: effects of biochar feedstock and pyrolysis temperature

Journal of Soils and Sediments - Tannery waste–contaminated soil has a high amount of several toxic chemicals and heavy metals including chromium (Cr), which makes it unsuitable for...     

Evaluation of wheat and maize evapotranspiration determination by direct use of the Penman–Monteith equation in a semi-arid region

The Penman–Monteith (PM) equation was introduced as one of the most reliable equations to determine crop ET_c, without using crop coefficient or ET_o values. In this study, the PM equation was evaluated using lysimeters in a semi-arid region for wheat and maize. Different equations for aerodynamic resistance (r _a) and canopy resistance (r _c) were tested in the PM equation and they were ranked using statistical analysis. It was shown that the combined method of r _a and r _c in FAO-56 does not lead to a good prediction of ET_c for wheat and maize in comparison with the lysimeter-measured data. The results indicated that a modified equation for r _c was the most accurate method for both wheat and maize. Using this equation, the suggested model of FAO-56 and another investigation for r _a led to the best results for wheat and maize, respectively. Furthermore, it was shown that the previously modified equation for r _c was newly modified as a function of vapor pressure deficit (VPD) and the results were as accurate as before. Therefore, an equation as a function of VPD can be used when solar radiation (R _n) is not available easily.     

Annual emissions of nitrous oxide and nitric oxide from a wheat–maize cropping system on a silt loam calcareous soil in the North China Plain

Nitrogen amendment followed by flooding irrigation is a general management practice for a wheat–maize rotation in the North China Plain, which may favor nitrification and denitrification. Consequently, high emissions of nitrous oxide (N₂O) and nitric oxide (NO) are hypothesized to occur. To test this hypothesis, we performed year-round field measurements of N₂O and NO fluxes from irrigated wheat–maize fields on a calcareous soil applied with all crop residues using a static, opaque chamber measuring system. To interpret the field data, laboratory experiments using intact soil cores with added carbon (glucose) and nitrogen (nitrate, ammonium) substrates were performed. Our field measurements showed that pulse emissions after fertilization and irrigation/rainfall contributed to 73% and 88% of the annual N₂O and NO emissions, respectively. Soil moisture and mineral nitrogen contents significantly affected the emissions of both gases. Annual emissions from fields fertilized at the conventional rate (600 kg N ha⁻¹ yr⁻¹) totaled 4.0 ± 0.2 and 3.0 ± 0.2 kg N ha⁻¹ yr⁻¹ for N₂O and NO, respectively, while those from unfertilized fields were much lower (0.5 ± 0.02 kg N ha⁻¹ yr⁻¹ and 0.4 ± 0.05 kg N ha⁻¹ yr⁻¹, respectively). Direct emission factors (EF_ds) of N₂O and NO for the fertilizer nitrogen were estimated to be 0.59 ± 0.04% and 0.44 ± 0.04%, respectively. By summarizing the results of our study and others, we recommended specific EF_ds (N₂O: 0.54 ± 0.09%; NO: 0.45 ± 0.04%) for estimating emissions from irrigated croplands on calcareous soils with organic carbon ranging from 5 to 16 g kg⁻¹. Nitrification dominated the processes driving the emissions of both gases following fertilization. It was evident that insufficient available carbon limited microbial denitrification and thus N₂O emission. This implicates that efforts to enhance carbon sink in calcareous soils likely increase their N₂O emissions.     

Amelioration of saline–sodic soil with gypsum can increase yield and nitrogen use efficiency in rice–wheat cropping system

A 2-year field experiment was conducted to determine crop yield and N use efficiency (NUE) from a saline–sodic soil (clay loam) with and without application of gypsum. Treatments included two N application rates (15% and 30%) higher than the recommended one to the normal soil, and gypsum added at 50% and 100% of soil gypsum requirement (SGR) to the saline–sodic soil, both cultivated with rice and wheat during 2011–2013. Results revealed a decrease in pH of saturated soil paste (pH_s), electrical conductivity of saturation extract (EC_e), sodium adsorption ratio (SAR) and exchangeable sodium percentage with N fertilizer along with gypsum application in saline–sodic soil. However, the effect was most prominent when gypsum was added at 50% of SGR. Crop yield and NUE remained significantly lower (p < 0.05) in saline–sodic-soils as compared to normal soil. However, gypsum application reduced this difference from 47% to 17% since both yield and NUE increased considerably. Crop yield and NUE remained higher for wheat than for rice. During first year, higher doses of N with gypsum application at 50% SGR proved most effective, whereas, in subsequent year, recommended N along with gypsum at 50% SGR became more profitable. All these results lead us to conclude that gypsum application can ameliorate saline–sodic soil thereby increasing crop yield and NUE.     

Effects of conservation tillage drills on soil quality indicators in a wheat–oilseed rape rotation: organic carbon,earthworms and water-stable aggregates

The effects of five conservation tillage drills with crop residue levels covering between 17% and 79% of the soil, and tillage depths ranging from 25 to 200 mm, were examined over 3 years. The tillage systems ranged from a relatively disruptive Farm System to a Low Disruption system, with three intermediate treatments labelled Sumo DTS, Claydon and Mzuri. The study involved field sites on a clay or clay loam soil, where winter wheat and oilseed rape were grown in rotation. In the clay field, the Mzuri and Low Disruption treatments, which produced the highest residue coverage, showed the greatest increase in surface total soil organic carbon (1.1 and 0.48 Mg C ha⁻¹, respectively) between years 1 and 3. The least disruptive tillage system also resulted in the highest density of earthworms (181–228 m⁻²), and the most disruptive system produced the lowest densities (75–98 m⁻²). In the third year, the least disruptive system also showed a higher proportion of water-stable aggregates (29.8%) than the other treatments (22.7%–25.3%). Linear regressions showed positive relationships of both soil organic carbon and earthworm density with surface residue cover, and of the proportion of water-stable aggregates with soil organic carbon.     

Influence of poultry manure–derived biochars on nutrients bioavailability and chemical properties of a calcareous soil

This study was conducted to investigate the effects of poultry manure (PM) and its derived biochars on chemical properties of a calcareous soil. PM and biochars prepared at 200°C (B200), 300°C (B300) and 400°C (B400) were applied to a calcareous soil at 2% level (w/w) and incubated for 150 days. Selected soil chemical properties and phosphorous, potassium, iron, manganese, zinc and copper availability and recovery were determined at 1, 15, 45 and 150 days of incubation. Soil nutrients availability, organic carbon (OC), electrical conductivity (EC) and cation exchange capacity (CEC) increased by addition of all organic substances. Biochars prepared at higher temperatures were more effective in increasing soil OC with higher durability compared to other treatments. The addition of PM and B200 decreased soil pH, whereas B400 increased it. Although the highest soil EC was observed in B300- and B400-treated samples in the early stages of incubation, the rate of increase in soil EC was higher for PM- and B200-treated soils compared to other treatments. It was concluded that biochar prepared at 300°C had the highest positive effect on nutrients availability and lasts longer in calcareous soil compared to the other produced biochars and PM.     

Influence of rotation and tillage on forage maize productivity,weed species,and soil quality of a fine sandy loam in the cool–humid climate of Atlantic Canada

Reduced tillage systems may be an option to allow rapid crop establishment in areas constrained by a short growing season, but such methods need to be adapted to soil tillage requirement and crop establishment needs. Rotation and tillage studies were conducted during a 6-year period on a fine sandy loam (Podzol) with silage maize (Zea mays L.) under the cool, humid climate, and relatively short growing season of Prince Edward Island, Atlantic Canada. The objective was to compare a continuous maize rotation with a maize–barley (Hordeum vulgare L.) rotation, using both no-tillage and conventional mouldboard ploughing for the maize, and to evaluate treatment effects on maize growth and productivity, weed populations, and soil quality. Plant population and maize yield were not consistently influenced by the tillage or rotation treatments. Mean maize yield ranged from 7.2 to 7.7 Mg ha⁻¹. An increasing density of weeds over the 6-year period, especially perennial species, was evident under no-tillage, compared to mouldboard ploughing. Except for slight changes in soil pH, spatial variation in extractable soil P, and a higher level of organic C and labile forms of C (microbial biomass and mineralizable C), soil chemical quality was similar among treatments. An apparent decline in soil physical quality, as indicated by a reduction in macro-porosity volume and increase in soil penetration resistance below the 8 cm soil depth, was evident under the no-tillage at the end of the 6-year period. However, macro-pore continuity was less affected by a reduction in tillage, while field measurements of soil hydraulic conductivity increased under no-tillage compared to ploughing. The latter result may be related to the observed increase in earthworm population where tillage was reduced. Use of rotational tillage resulted in an intermediate soil physical condition between continuous no-tillage and ploughing. Overall, no-tillage appears a promising strategy to facilitate a fast and early establishment of maize on sandy loam soils in Atlantic Canada, but some ongoing monitoring of the soil physical condition would be required.     

Long-term effects of fertilization and manuring on productivity and soil biological properties under rice (Oryza sativa)–wheat (Triticum aestivum) sequence in Mollisols

Long-term effects of chemical fertilizers and farmyard manure (FYM) in rice (Oryza sativa)–wheat (Triticum aestivum) cropping system were monitored for two consecutive years after 38 and 39 years on productivity and soil biological properties of Mollisols. The study encompasses varying chemical fertilizer levels of optimum fertilizer rate (120, 26 and 37 kg ha^?1 N, P and K, respectively) for both the crops. The treatments were application of 50% NPK, 100% NPK, 150% NPK, 100% NPK + hand weeding (HW), 100% NPK + Zn, 100% NP, 100% N, 100% NPK + 15 t FYM ha^?1, 100% NPK(-S) and unfertilized control. The rice and wheat yields were highest with 100% NPK + 15 t FYM ha^?1. This treatment also gave maximum and significantly more counts of bacteria, fungi and actinomycetes in soil than all the other treatments after crop harvest. The soil microbial biomass C (410.0 and 407.5 µg g^?1) and N (44.53 and 48.30 µg g^?1) after rice and wheat, respectively, were highest with 100% NPK + 15 t FYM ha^?1, which were significantly higher over all the other treatments. The activities of soil enzymes like dehydrogenase, acid and alkaline phosphatase, arylsulphatase and urease and CO₂ evolution rate with 100% NPK + 15 t FYM ha^?1 were also found significantly higher over the other treatments. Fertilizer treatments with 100% NPK and 150% NPK were comparable and significantly better than application of 50% NPK, 100% N, 100% NP and 100% NPK(-S) in various studied soil biological properties. Integrated use of 100% NPK with FYM sustained the higher yields and soil biological properties under rice–wheat cropping system in Mollisols. Application of Zn and hand weeding with 100% NPK were found better over 100% NPK alone in rice and wheat productivity. Imbalanced use of chemical fertilizers had the harmful effect on soil biological health.     

Annual variation in δC values of maize and wheat: Effect on estimates of decadal scale soil carbon turnover

On sites where C4-plants have replaced C3-plants, changes in soil δ¹³C allow the turnover of C3- and C4-derived C to be separated. Studies of decadal scale turnover of soil C following conversion to C4-plants generally lack δ¹³C values for previous C4-residue inputs and assume that estimates of C4-derived soil C to be based on a fixed δ¹³C value. Further assumptions are that changes in the initial (time-zero) soil δ¹³C values are insignificant following conversion to C4-plants. We tested these assumptions by measuring: 1) the δ¹³C of annual samples of silage maize biomass (C4-plant) and winter wheat grains (C3-plant) grown during 1988 to 2006, and 2) the δ¹³C of soil kept under bare fallow during 1956 to 1983. The δ¹³C of plants was related to climate variables, and the impact of maize δ¹³C was based on estimates of maize-derived soil C using different approaches to establish the δ¹³C in maize inputs. The δ¹³C of both maize and wheat decreased with time, but the rate of change and annual variations were considerably larger for wheat than for maize. Maize as well as wheat δ¹³C was best related to year (probably reflecting a decrease in atmospheric δ¹³C) and the water balance during the active growth period. Using the smallest (−12.44‰) and the largest (−11.26‰) δ¹³C measured during 1988 and 2006, estimates of maize-derived C in soil after 18 years ranged from 13.2% to 14.2% of the soil total C. Despite a loss of 31% of the soil C pool under bare fallow, the increase in soil δ¹³C was significant only at P < 0.10. We conclude that annual variations in maize δ¹³C values and changes in the δ¹³C of the soil C fraction derived from the pre-conversion C3-vegetation have only little impact on estimates of maize-derived soil C that cover a few decades. For estimates covering several decades to centuries, the subtle but consistent changes in plant and soil δ¹³C need to be accounted for. The variability in δ¹³C in wheat grains suggest that the use of any fixed δ¹³C value for C3-residues in estimates of C turnover in soils on which C4-plants have been replaced by C3-plants can be associated with considerable uncertainty.     

Effect of a decade-long chemical fertilizers and amendments application on potassium fractions and yield of maize​–wheat in an acid Alfisol

Effect of long-term addition of chemical fertilizers with or without amendments was studied on different forms of potassium and the yield of maize and wheat. Continuous application of chemical fertilizers and amendments for 40 years influenced different fractions of potassium significantly. Integrated use of a balanced dose of chemical fertilizer, with farmyard manure (FYM) or lime, sustained higher yields of maize and wheat in comparison to inorganic fertilizers alone. Application of urea (100%) N alone for 40 years resulted in zero yield level. Continuous application of chemical fertilizers either alone or in combination with FYM or lime influenced different fractions of potassium significantly. Continuous cropping without fertilization resulted in depletion to the order of 21.5%, 16.6%, 11.7%, and 5.5% in water-soluble, exchangeable, 0.5 N HCl extractable, and non-exchangeable K, respectively. Different fractions of potassium were found to be positively and significantly correlated with grain and stover/straw yield of maize and wheat.     

Responses of soil nematode community structure to different long-term fertilizer strategies in the soybean phase of a soybean–wheat–corn rotation

The impact of long-term application of fertilizers in soybean fields on soil nematode community structure was studied. The long-term application model of fertilizers lasted 13 years in a soybean–wheat–corn rotation, and included three treatments: no fertilizer (NF), chemical fertilizer (urea and ammonium phosphate, CF), and pig manure combined with chemical fertilizer (MCF). The soil nematode community structures and ecological indices were determined from soil samples taken at five soybean growth stages from May to October in the soybean phase of the rotation. Fertilizer application had significant effects on abundance of plant parasites, bacterivores and fungivores (P < 0.05), but had no significant effects on total nematodes and omnivores-predators. Abundance of plant parasites was higher in NF than in MCF and CF, and abundance of bacterivores was highest in MCF. Fertilizer application significantly affected Plant-parasitic Nematode Maturity Index (PPI) and Nematode Channel Ratio (NCR) ecological indices (P < 0.05). Shannon–Weaver Index (H′) and Species Richness (SR) indices were higher in MCF than in either NF or CF. The abundances of total nematode and plant parasites showed increasing trend with soybean growth in all three treatments. This is probably due to soil environment being more suitable for soil nematode survival with more food available for plant parasites as the soybean grows. Soybean growth stage significantly affected the H′, Free Living Nematode Maturity Index (MI) and PPI. Bacterivores significantly correlated with soil nutrient status suggesting that they could be used as a potential indicator of soil fertility.     

Penicillium bilaii effects on maize growth and P uptake from soil and localized sewage sludge in a rhizobox experiment

With P being a non-renewable resource, the use of microbial inoculants and waste products for more efficient and sustainable P use in plant production has been proposed. We investigated the ability of Penicillium bilaii to mobilize P in a low-fertility soil with or without amendment of sewage sludge as additional P source. Maize was grown for 27 days in rhizoboxes enabling studies of root growth in addition to plant and soil parameters. P. bilaii was inoculated either at the seed or the sewage sludge patch. At early growth stages, P. bilaii inoculation of seeds increased maize shoot length. However, at the end of experiment, the effect had ceased. Root growth was increased by seed P. bilaii inoculation alone and in combination with sewage sludge, whereas patch inoculation was less effective. Colonization studies performed at harvest showed that P. bilaii could not be detected in the maize rhizosphere but stayed at the place of inoculation. In sewage sludge patches, the growth of Penicillium strains other than P. bilaii was stimulated; hence, using sewage sludge for combined P resource and carrier of microbial inoculants is discussed. Unexpectedly, the greater root development of seed-inoculated plants did not result in increased plant P uptake and neither did inoculation at the sewage sludge patch. This study raises the question if the soil P status can be too low for a beneficial effect of additional early root growth and thus a beneficial effect of seed inoculation of P. bilaii.     

Effect of conservation agriculture on soil organic and inorganic carbon sequestration and lability: A study from a rice–wheat cropping system on a calcareous soil of the eastern Indo-Gangetic Plains

Increasing soil carbon (C) in arable soils is an important strategy to achieve sustainable yields and mitigate climate change. We investigated changes in soil organic and inorganic carbon (SOC and SIC) under conservation agriculture (CA) in a calcareous soil of the eastern Indo-Gangetic Plains of India. The treatments were as follows: conventional-till rice and wheat (CT-CT), CT rice and zero-till wheat (CT-ZT), ZT direct seeded rice (DSR) and CT wheat (ZT-CT), ZTDSR and ZT wheat without crop residue retention (ZT-ZT), ZT-ZT with residue (ZT-ZT+R), and DSR and wheat both on permanent beds with residue (PB-PB+R). The ZT-ZT+R had the highest total SOC in both 0–15 and 15–30 cm soil layers (20% and 40% higher (p < .05) than CT-CT, respectively), whereas total SIC decreased by 11% and 15% in the respective layers under ZT-ZT+R compared with CT-CT. Non-labile SOC was the largest pool, followed by very labile, labile and less labile SOC. The benefits of ZT and residue retention were greatest for very labile SOC, which showed a significant (p < .05) increase (~50%) under ZT-ZT+R compared with CT-CT. The ZT-ZT+R sequestered ~2 Mg ha⁻¹ total SOC in the 0–15 cm soil layer in 6 years, where CT registered significant losses. Thus, the adoption of CA should be recommended in calcareous soils, for C sequestration, and also as a reclamation technique.     

Organic waste amendment effects on soil microbial activity in a corn–rye rotation: Application of a new approach to community-level physiological profiling

The role of phosphorus (P) application and arbuscular mycorrhizal fungi (AMF) on growth, arsenic (As) and P accumulation in lettuce plants growing in an As-polluted soil (total As 250 mg kg⁻¹), was investigated. In particular, it was tested whether application of a commercial inoculum (CI), with (+P at 90 kg P ha⁻¹) and without (−P at 0 kg P ha⁻¹) P fertilizer, supported greater plant growth and provided more P, enhancing As tolerance, than indigenous fungi alone. The influence of these treatments on As and P availability in the rhizosphere and bulk soils was also investigated. Greenhouse pot experiments were established where plants were grown with and without commercial inoculum (+CI, −CI) in unsterilized conditions. Inoculation with commercial inoculum and P application together considerably increased plant biomass, by enhancing host plant P nutrition and lowering shoot and root As concentrations compared to plants inoculated only with native AMF. In the rhizosphere of +CI+P plants there was P soil depletion compared to −CI+P. The results evidenced that, with P addition, inoculation with commercial inoculum alleviated the toxicity of excessive As by improving P nutrition without increasing As concentrations in the plant, emphasizing the role of beneficial microbes and P fertilizer to improve soil fertility in As-contaminated soil.